Digital x-ray diagnosis and evaluation of dental disease

ABSTRACT

A method for diagnosis and evaluation of tooth decay comprises: locating in an x-ray image the contour of the dento-enamel junction (DEJ); measuring optical density along contours substantially parallel to and on either side of the DEJ contour; and calculating at least one numerical decay value from the measured optical densities. A method for diagnosis and evaluation of periodontal disease comprises: measuring in an x-ray image a bone depth (BD) relative to the position of the cemento-enamel junctions (CEJs) of adjacent teeth; measuring bone density along a contour between the adjacent teeth; and calculating a numerical crestal density (CD) value from the measured bone density. Calibration standards may be employed for facilitating calculation of the numerical values. A dental digital x-ray imaging calibration method for at least partly correcting for variations of the optical densities of images acquired from the dental digital x-ray imaging system.

The present application is a continuation of U.S. patent applicationSer. No. 11/652,822, filed Jan. 12, 2006, now U.S. Pat. No. 8,417,010.U.S. patent application Ser. No. 11/652,822 is an application claimingthe benefit under 35 USC Section 119(e) of U.S. Provisional PatentApplication Ser. No. 60/758,829, filed Jan. 12, 2006. The presentapplication is an application claiming the benefit under 35 USC Section119(e) of U.S. Provisional Patent Application Ser. No. 60/758,829, filedJan. 12, 2006. The present application is based on and claims priorityfrom these applications, the disclosures of which are hereby expresslyincorporated herein by reference in their entirety.

BACKGROUND OF INVENTION

The field of the present invention relates to diagnosis and evaluationof dental disease, including dental caries and periodontal disease. Inparticular, systems and methods are described herein for analysis ofdigital x-ray images for diagnosis and evaluation of dental caries orperiodontal disease.

Diagnosis and evaluation of dental disease (such as dental caries,periodontal disease, or dental abscesses) based on visual inspection ofx-rays (either film or digital) is hampered by variations among film,x-ray sources, imaging x-ray sensors, display devices, subjectiveinterpretation by clinicians, and so on. At least one earlier attempthas been made to address such variations by analysis of digital x-rayimages for detection of dental caries (i.e. tooth decay or cavities),and is described in U.S. Pat. No. 5,742,700 issued to Yoon et al. (saidpatent is hereby incorporated by reference as if fully set forthherein). However, a subsequent study indicates the earlier system maynot be sufficiently reliable in its diagnosis and evaluation of decay(Kang et al., Korean J Oral Maxillofacial Radiology v32 pp 187-194(2002), which is hereby incorporated by reference as if fully set forthherein).

Therefore, a need exists for more reliable systems and methods fordiagnosis and evaluation of dental or periodontal disease.

BRIEF SUMMARY OF THE INVENTION

A method for diagnosis and evaluation of tooth decay comprises: locatingin an x-ray image the contour of the dento-enamel junction (DEJ);measuring optical density (relative to the absorption of x-rays in theelectromagnetic spectrum used for radiographs—i.e. radiodensity) alongcontours substantially parallel to and on either side of the DEJcontour; and calculating at least one numerical decay value from themeasured optical densities. A method for diagnosis and evaluation ofperiodontal disease comprises: measuring in an x-ray image a bone depth(BD) relative to the position of the cemento-enamel junctions (CEJs) ofadjacent teeth; measuring bone density along a contour between theadjacent teeth; and calculating a numerical crestal density (CD) valuefrom the measured bone density. Calibration standards may be employedfor facilitating calculation of the numerical values.

The present invention is also directed to a dental digital x-ray imagingcalibration method for at least partly correcting for variations of theoptical densities of images acquired from the dental digital x-rayimaging system. The calibration method of the present invention mayinclude five exemplary basic steps. The first step is providing at leastone calibration block or standard that simulates dental tissues. Thesecond step is acquiring an image of the calibration block or standardfrom the dental digital x-ray imaging system. The third step iscalculating a calculated numerical decay value. The fourth step iscomparing the known numerical decay value and the calculated numericaldecay value. The fifth step is calibrating the dental digital x-rayimaging system by adjusting the dental digital x-ray imaging system sothat the calculated numerical decay value approaches the known numericaldecay value.

Objects and advantages pertaining to digital x-ray diagnosis andevaluation of dental or periodontal disease may become apparent uponreferring to the exemplary embodiments illustrated in the drawings anddisclosed in the following written description and/or claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1-4 are dental x-ray images showing areas of suspected decay.

FIGS. 5-15 are images that illustrate use of a software algorithm fordiagnosing and evaluating decay from the digital dental x-ray image.

FIGS. 16-18 are dental x-ray images showing areas of suspected decayanalyzed with the software algorithm.

FIGS. 19-21 are charts that illustrate optical density plots along theDEJ corresponding to FIGS. 16-18, respectively.

FIGS. 22-24 are charts that illustrate integration of areas of dips inthe optical density plots of FIG. 19-21, respectively.

FIGS. 25-30 are images that illustrate selection of areas of a dentalx-ray image for analysis.

FIGS. 31-38 are images that illustrate results of the analysis indicatedin FIGS. 25-30.

FIGS. 39-42 are photographs and a radiograph illustrating the clinicalfindings and treatment corresponding to the dental x-ray images of FIGS.25-30 and the analysis of FIGS. 31-38.

FIGS. 43-51 are images and charts that illustrate selection and analysisof areas of a dental x-ray image.

FIG. 52 is a photograph illustrating the clinical findings and treatmentcorresponding to the dental x-ray images and analysis of FIGS. 43-51.

FIGS. 53-60 are images that illustrate use of a software algorithm fordiagnosing and evaluating decay from the digital dental x-ray image.

FIGS. 61A and 61B illustrate aluminum step wedge radiographiccalibration blocks.

FIG. 62 is a radiograph illustrating the composite structure of teeth.

FIGS. 63 and 64 are schematic cross sectional diagrams of a tooth withdecay.

FIGS. 65 and 66 are radiographs showing samples of materials forsimulating enamel and dentin, respectively.

FIG. 67 is a schematic diagram of a composite calibration block.

FIG. 68 is a radiograph showing composite calibration blocks.

FIG. 69 shows optical density curves measured from the radiograph ofFIG. 68.

FIG. 70 is a schematic diagram of a composite calibration block with adefect.

FIGS. 71 and 72 are radiographs showing composite calibration blockswith defects.

FIGS. 73 and 74 are charts that show optical density curves measuredfrom the radiographs of FIG. 72.

FIGS. 75 and 76 are radiographs showing healthy lamina dura bone.

FIGS. 77-80 are radiographs showing examples of lamina dura bone damagedby periodontal disease.

FIGS. 81-87 illustrate use of a software algorithm for diagnosing andevaluating periodontal disease from the digital dental x-ray image.

FIGS. 88 and 89 are optical density traces from the radiographs of FIGS.81-87.

FIG. 90 is a chart that illustrates calculation of crestal bone depthfrom an optical density trace.

FIGS. 91 and 92 are charts that illustrate calculation of crestal bonedensity from an optical density trace.

FIGS. 93 and 94 are images that illustrate crestal bone depth and bonedensity obtained using the software algorithm.

FIG. 95 is a radiograph with a site of suspected periodontal diseaseindicated.

FIGS. 96-99 are images that illustrate use of a software algorithm fordiagnosing and evaluating periodontal disease from a digital dentalx-ray image.

FIG. 100 is a density plot measured from the radiograph of FIGS. 95-99.

FIGS. 101 and 102 are charts that illustrate calculation of bone depthand bone density from the plot of FIG. 100.

FIG. 103 is a radiograph with calculated bone depth and bone densityvalues displayed.

FIGS. 104-108 are radiographs illustrating use of the software algorithmfor evaluating periodontal disease.

FIGS. 109-111 are radiographs with displayed values for bone depth andbone density.

FIG. 112 is a flow chart showing a simplified exemplary embodiment of adental digital x-ray imaging calibration method of the presentinvention.

The embodiments shown in the figures are exemplary, and should not beconstrued as limiting the scope of the present disclosure and/orappended claims.

DETAILED DESCRIPTION OF THE INVENTION

The primary economic consideration when converting to digital dentalimaging is the accurate diagnosis of primary decay, directly relatedsecondary decay conditions, or other dental diseases such as periodontaldisease or endodontic abscesses. A typical dental practice profile inthe U.S. comprises one dentist or doctor (terms used interchangeablyherein) and one hygienist generating around $500K or more. Approximately60% or more of that revenue is derived from the diagnosis of decay orconditions secondary to decay. Any inability to accurately diagnosedecay or any other dental disease using dental imaging thereforerepresents a significant opportunity for loss of revenue, and typicallyprofit as well, in addition to putting the patient at risk for a missed(e.g., false negative) or inaccurate (e.g., false positive) diagnosis.

Conversion to digital dental x-ray imaging and analysis may be employedfor improving the accuracy of dental disease diagnosis, and may offerother practical benefits as well. For example, the use of digitalimaging and analysis may reduce the time required for making adiagnosis, benefiting both dentist and patient. Images may be retrievedelectronically for viewing or analysis quickly and remotely withoutsearching for x-ray films. Patient may be more accepting of a diagnosismade by digital methodologies because they can better visualize theirown condition.

However, existing digital imaging and analysis systems have beendemonstrated to be no more accurate than visual evaluation oftraditional x-ray film images. (See for example U.S. Pat. No. 5,742,700to Yoon, and Kang et al., “Computer-aided proximal caries diagnosis:correlation with clinical examination and histology,” Korean Journal ofOral and Maxillofacial Radiology v32 pp 187-194 (2002), both of whichare hereby incorporated by reference as if fully set forth herein.) Inanother report (Smith, K.; “Caries Detection; At Best an InexactScience”; Global Dental Newsjournal; www.global-dental.com/clinical.htmland www.global-dental.com/clinical_(—)2.html), significantly higherfalse-positive rates are found for visual evaluation of digital images(11% false positives) relative to visual evaluation of film images (7%false positives). As already stated above, any inability to accuratelydiagnose decay, whether arising from inaccurate visual evaluation ofx-ray film or inaccurate analysis of digital x-ray images, represents asignificant opportunity for loss of revenue, and typically profit aswell. Furthermore, inaccurate diagnosis may undermine the patient'sconfidence in the doctor's skill or judgment, or lead to patienthesitation regarding the doctor's future diagnoses or treatmentrecommendations.

From a clinician's perspective, an accurate diagnosis of decay includesaccurate “staging” of the decay. Stage I and Stage II decay exist onlyin the enamel of the affected tooth, with Stage I decay penetrating lessthan 50% through the enamel toward the dentin, and with Stage II decaypenetrating more than 50% toward the dentin (but still not reaching thedentin). Stage III and Stage IV decay exist in both the enamel and thedentin, with Stage III penetrating less than 50% through the dentintoward the nerve space, and with Stage IV decay penetrating more than50% through the dentin. The stage of the decay and the age and clinicalhistory of the patient are considered together in determining theappropriate clinical course. For example, for a teenager with rapidlyprogressing or widespread Stage I, decay should be treated aggressivelywith fillings to prevent penetration of decay into the dentin. Incontrast, an adult with radiographically detectable Stage II decay at aroutine six-month exam may be appropriately treated by watching ratherthan filling. Stage III decay almost always requires fillings fortreatment, and if not accurately diagnosed will likely progress to StageIV decay. Stage IV decay may require even more extensive treatment, suchas a root canal or a very deep filling with a pulp cap for reducingpainful post-operative sensitivity. In each of these cases, an accuratediagnosis is necessary to inform the patient and to plan appropriatetreatment.

Several exemplary dental x-ray images are shown in FIGS. 1-4,illustrating the difficulty of accurately diagnosing decay from suchimages. FIGS. 1 and 2 show teeth #3, #4, and #5 (specific teeth may bereferred to hereinafter by number only). It is difficult to discern fromthese images the extent of interproximal decay between these teeth, orif decay is even present. Likewise, in FIGS. 3 and 4, it is difficult toevaluate interproximal decay (if any) between #30 and #31. These directdigital images were “enhanced” for visual interpretation on a displaymonitor. Critical data is often washed out by the x-ray capture andimage display process, making decay difficult to detect or evaluate.Other difficulties arise from: i) lack of calibration of x-ray output,which typically degrades with the age of the instrument; ii) neitherx-ray film nor digital x-ray imaging sensors are typically optimizedrelative to each x-ray machine (non-optimization of x-ray film ordigital x-ray imaging sensors relative to each x-ray machine); iii)existing x-ray film chemical processing and x-ray image softwareprocessing are optimized for visual inspection, but not necessarily fordecay detection (non-optimization of x-ray film chemical processing andx-ray image software processing for visual inspection, but notnecessarily for decay detection); iv) degradation of image quality asthe display monitor ages; and v) variation among different operatorsacquiring the images or different observers interpreting the images.

It may be preferable to develop a diagnostic procedure or protocol usingthe native data captured from film or digital sensors and pre-processedseparately from the visual display for optimum dental disease detection.Such an approach might be designated for convenience as Computer AidedDental Diagnostics (CADD). Such procedure or protocols might include: i)periodic (i.e. yearly) calibration of the x-ray source and digital x-rayimaging sensor; ii) including both normal and diseased tissue (i.e.normal tooth and decay) in the calibration procedure; iii) use ofsoftware algorithms to determine the presence or extent of decay; andiv) providing a numerical value (a numerical decay value calculated fromthe measured optical densities) that correlates with the extent of decaypresent to further assist the clinician in making an accurate diagnosisor appropriate treatment plan.

One exemplary software algorithm for detecting and evaluating toothdecay may be designated for convenience as CarieScan CADD. The algorithmuses the native x-ray image data for processing. The software analyzesthe image to detect decay based upon algorithms which may utilize edgedetection techniques, pattern recognition techniques, individual toothgeometry data, or other factors (including patient data). The results ofthe software analysis may be superimposed onto a dental x-ray image, butare obtained in a manner independent of any processing of the image forvisual presentation or interpretation. FIGS. 5-15 illustrate use of theCarieScan algorithm. Upon activation (FIG. 5), a dental x-ray image isdisplayed, along with a user-movable cursor and a dynamic numericaldisplay showing maximum and local values for a numerical decay value.Both displayed numerical values may be zeroed before any analysisoccurs. As shown in FIGS. 6 and 7, a user uses the cursor to mark theends of a segment of the dentin-enamel junction (DEJ). Once the ends aremarked, the software analyzes the raw image data (not the processedversion of the data used to generate the display) to locate the DEJ andto generate a numerical decay value that may vary with position alongthe DEJ (FIG. 8). A 0-100 scale is used in this example, with highernumerical values corresponding to greater extent of decay. Any scale,however, with any desired magnitude or directionality may be employed.Once the analysis is complete (described further herein below), thenumerical display shows a local (at the cursor location) numerical decayvalue in one box (the left in this case) and a maximum numerical decayvalue for the marked portion of the DEJ in the other box. The cursor maybe moved along the DEJ in the image while the user notes the location(s)of high numerical decay values (FIGS. 9-15).

Audible alarms, color-coded text or graphics in the display, or othersuitable means may be employed for alerting the user to detected decay.These may be coded to correspond to varying numerical decay values,based on any suitable or desirable criteria. Many scaling options arepossible and may be employed. For example, a scheme may be employedwherein: i) green indicates decay that has not yet penetrated throughenamel; ii) yellow indicates decay that has penetrated through enamelinto dentin less than about 0.5 mm or less than about 50% of thethickness of adjacent enamel; iii) orange indicates decay that haspenetrated into dentin more than about 0.5 mm but less than about 1.0mm, or more than about 50% but less than about 100% of the thickness ofadjacent enamel; and iv) red indicates decay that has penetrated intothe dentin more than about 1.0 mm or more than about 100% of thethickness of adjacent enamel.

Analysis of the raw x-ray image data to yield numerical decay valuesfocuses on the densities of enamel and dentin along the dentin-enameljunction (DEJ). In FIG. 16, a tooth is analyzed that is unaffected bydecay, with the DEJ intact. Once the user clicks near the ends of theDEJ (as in FIGS. 6 and 7), the analysis algorithm first locates thecontour of the DEJ. The optical density is then measured alongsubstantially parallel contours, one just outside the DEJ in the enamel,the other just inside the DEJ in the dentin. The optical density(equivalently, radiodensity) is plotted as a function of distance alongthe DEJ in FIG. 19. In a tooth unaffected by decay, the two densitycurves are substantially flat (indicating substantially constantdensity), with the enamel density larger than the dentin density. Thenumerical density of intact enamel is arbitrarily normalized to 100% inthis example. In FIG. 17, a tooth is analyzed that shows signs of onlyearly-stage decay penetrating only partly into the enamel.

Results of the corresponding analysis are shown in FIG. 20. The densitycurve for the dentin remains substantially flat, while a dip is seen inthe density curve for the enamel, indicating that a portion of theenamel near the DEJ has been affected by decay. The curves arenormalized, with the flat portions of the enamel density curve being setto 100%.

In FIG. 18, analysis of an area of more advanced decay is illustrated.The corresponding density curves in FIG. 21 exhibit extensive dips inboth enamel and dentin density curves. The width of the affected area(i.e. the length of the dip along the DEJ) is larger in the dentin. Thisarises from differing pathophysiology of the respective decay processesin enamel and dentin. The decay process in enamel is diet-driven:bacteria rely on external nutrients (such as dietary sugars), and theacids produced by their metabolic activity drives the decay process. Thedecay “tunnels” through the enamel, often along developmental grooves onbiting surfaces or at contact points between teeth where acids canaccumulate; open areas of the enamel are typically less prone to decay.Dentin-based decay is not diet driven; dentin contains proteins thatnourish bacteria independent of the patient's diet. The bacteria presentin the dentin engage in a different breakdown process. Decay in dentinis essentially a surface process, which results in a substantiallyhemispherical geometry radiating into the dentin from the point ofpenetration through the enamel. The remaining enamel effectively shieldsthe bacteria from the protective properties of saliva, therebyfacilitating the decay process.

The density curves for enamel and dentin along the DEJ exhibit distinctqualitative features depending on the extent of the decay process. Thecurves are analyzed by the software algorithm to yield a numerical decayvalue. An exemplary analysis procedure includes: i) integration of thearea of a dip in the normalized enamel density curve; ii) integration ofthe area of a dip in the normalized dentin density curve; iii)application of relative scaling factors to the two integrated values(typically weighting any dentinal decay more heavily; iv) addingtogether the integrated, scaled values; and v) multiplying by anotherscale factor to normalize to a desired scaling range.

When this procedure is applied to the density curves from a toothsubstantially free of decay (as in FIG. 19), integrated values of aboutzero are obtained (as in FIG. 22). A numerical decay value of zero wouldindicate that no decay is present. Application of the procedure isillustrated in FIG. 23 for the curves shown in FIG. 20. Integration ofthe enamel curve yields a value of 90, and integration of the dentincurve yields a value of 0. Dividing the sum of these two values by ascaling factor of 10 yields a numerical decay value of 9, indicating alow probability of decay requiring interventional treatment. Applicationof the analysis procedure to the density curves of FIG. 21 isillustrated in FIG. 24. An integrated value of 285 is obtained forenamel-borne decay adjacent to the DEJ, while an integration value of299 is obtained for dentin-borne decay adjacent to DEJ, which is thenmultiplied by a relative scaling factor of 2 since dentin-borne decay isthe more significant decay process. The sum 285+(299×2)=883 is dividedby the scaling factor of 10 to obtain a numerical decay value of 88,which indicates highly active decay requiring treatment as soon aspossible.

FIGS. 25-30 illustrate a remaining portion of the procedure foranalyzing the entire x-ray image. The user clicks twice on each DEJsegment to be analyzed and, upon the second click, the software (in thebackground and as described hereinabove) locates the DEJ, plots theenamel and dentin densities along contours substantially parallel to andbracketing the DEJ, integrates any dips in the plots, calculatesnumerical decay values as a function of position along the DEJ, anddisplays the local numerical value (in the left display box) and themaximum numerical decay value (right display box). This is repeated foreach DEJ segment to be analyzed. Once the desired DEJ segments have beenmarked and analyzed, the user may move the cursor over the image todisplay the numerical decay values obtained, as in FIGS. 31-37.Functionality may be added for enabling display of maximum numericaldecay values for each analyzed DEJ segment, as shown in FIG. 38. Basedon the maximum numerical decay values calculated, it is determined that#4, #5, #30, and #31 are in need of treatment. The actual clinicalfindings and treatment are illustrated in FIGS. 39-42.

It should be noted that the specific numerical values obtained uponintegration of the areas of any dips in the density curves areunit-dependent. Appropriate weighting and scaling factors are chosen,based at least in part on the units employed in the optical densityplots, to yield numerical decay values falling within a desired range ofvalues. Any suitable unit and scaling scheme may be employed and shallfall within the scope of the present disclosure.

Each tooth has a specific decay pattern, influenced by tooth location,enamel thickness, enamel geometry, adult versus pediatric teeth, and soforth. The software algorithm may be adapted to account for suchinfluences. For example, weighting or scaling factors may differdepending on these various influences so as to accordingly alter thecalculated numerical decay values. Such influences may be incorporate bymanual identification (tooth number, patient age, DEJ contour, and so onmanually entered by user), or may be incorporated automatically by thesoftware through optical pattern recognition, edge detection of all orpart of DEJ, previously measured and stored calibration standards,statistical analysis, or through other means.

An example of analysis of an x-ray of pediatric teeth is illustrated inFIGS. 43-51. Different scaling factors of 2 and 5 are used formultiplying the integrated areas of the enamel and dentin traces,respectively. These larger factors reflect the smaller size and thinnerenamel characteristic of pediatric teeth, and the need for earlierdetection and intervention. From the traces for #S is calculated(174×2+76×5)/10=73, and for #T is calculated (91×2+5×5)/10=21. Differentlevels may be assigned for color coding or audible alarms for pediatricteeth versus adult teeth. For example, for pediatric teeth: i) greenindicates decay that has not yet penetrated through enamel; ii) yellowindicates decay that has penetrated through enamel to level of dentinless than about 0.25 mm or less than about 50% of enamel thickness; iii)orange indicates decay that has penetrated into dentin greater thanabout 0.25 mm and less than about 0.5 mm or greater than about 50% andless than about 100% of enamel thickness; and iv) red indicates decaythat has penetrated into the dentin more than about 0.5 mm or more thanabout 100% of enamel thickness. The corresponding clinical presentationis shown in FIG. 52.

In another embodiment of a software algorithm for diagnosis of toothdecay, use of edge detection algorithms in combination with patternrecognition functions for mapping the entire DEJ contour is illustratedin FIGS. 53-60. Two points near the DEJ are marked by the user (FIGS. 53and 54). The software algorithm then locates the DEJ contour (FIG. 55),and computes numerical decay values along the DEJ (FIG. 56). This isrepeated for other teeth in the x-ray image (FIG. 57). Once the analysisis complete, numerical decay values are displayed as the user moves acursor over the image (FIGS. 58-60). Other approaches may be employed aswell. For example, the DEJ could be manually traced by a user.

The successful implementation of software algorithms disclosed hereindepends to some extent on suitable calibration of the optical densitiesof the acquired images. Dental digital x-ray imaging processes aresubject to multiple variables, including but not limited to: i)intensity variation among different x-ray sources (or just the aging ofindividual x-ray sources); ii) sensitivity variation among differentx-ray imaging sensors, and with aging of individual x-ray sensors; iii)variations arising from different image processing algorithms orprotocols; iv) variation among different display devices (or just theaging of individual display devices); v) subjective operator judgment inthe final interpretation of x-ray images; and vi) other variables.Calibration “blocks,” or standards, are used to try to at leastpartially correct for some of these variations.

One example of an existing calibration block is an aluminum “stepwedge,” as illustrated in FIGS. 61A and 61B. Linear angled wedges aresometimes employed as well. However, current calibration methodologiesdo not typically account for tooth size, tooth location, tooth distancefrom the imaging plane, intervening layers of tissue, the compositestructure of teeth, or the effect these factors have on clinicaldiagnostics. A dental diagnosis needs a calibration standard thatsimulates dental tissues and diseases of those tissues. Such acalibration standard should radiographically simulate the true compositestructure of teeth (i.e. enamel plus dentin plus pulp; FIG. 62), shouldgeometrically and dimensionally simulate the structure of teeth, andshould simulate dental pathology, both in size and location. Suchrealistic calibration devices could be used in conjunction with imageanalysis, edge detection, or pattern recognition algorithms to achieve afar higher level of accuracy in clinical diagnosis. Accordingly, dentalx-ray calibration methodologies disclosed herein simulate dentalpathology in simulated teeth, factoring in pathology size, radiodensity,and location through the radiodense layers of the teeth. A rectangular(or other suitable cross-sectional shape) composite calibrationstructure is fabricated for simulating enamel, dentin, and variousdental pathologies, and then an x-ray image of the compositecalibrations structure is analyzed as described hereinabove.

As shown in the schematic cross-sectional diagram of a tooth in FIG. 63,x-rays pass through about 7 mm of enamel to show decay in the enamelnear the DEJ near the proximal contact point with an adjacent tooth. Inthe schematic cross-sectional diagram of a tooth in FIG. 64, it is seenthat x-rays pass through about 2 mm of enamel and about 5 mm of dentinto show decay in the dentin. Materials are chosen that simulate theradiodensity of enamel (FIG. 65; radiographically the most densematerial in the human body) and the radiodensity of dentin (FIG. 66;radiographically the second most dense material in the human body).Examples of suitable materials that can be used are plastics impregnatedwith defined levels of radiopaque compounds (such as barium) to simulateenamel or dentin or the use of light-activated dental filling materialsthat contain varying levels of radiopaque compounds. A rectangularcomposite block is fabricated from simulating materials as shown in FIG.67, with 1 mm of the enamel-density material surrounding a 5 mm thicklayer of the dentin-density material. X-ray images of such blocks areshown in FIG. 68, and the optical densities measured along either sideof the simulated DEJ are shown in FIG. 69. The curves of FIG. 69resemble those curves extracted from the actual patient x-ray and shownin FIGS. 19 and 22.

Defects of various sizes may be cut into the composite calibrationblocks to simulate tooth decay or caries. A composite simulation blockis shown in FIG. 70 with a 3 mm diameter cylindrical defect penetratingthe enamel and entering the dentin. Simulated defects of various sizesmay be employed. FIG. 71 shows x-rays of a composite calibration blockwith a 1 mm cylindrical defect and a composite calibration block with a3 mm cylindrical defect. The optical densities are measured from theimage along the lines parallel to the simulated DEJ in the compositecalibration structure as shown in FIG. 72, and the results are plottedin FIGS. 73 and 74. The 1 mm defect yields a directly measurable widthof about 0.8 mm in both the enamel and the dentin. The integrated dip inthe enamel curve yields a value of 41, while the integrated dip in thedentin curve yields a value of 73. The 3 mm defect yields a directlymeasurable width of about 2.6 mm in both the enamel and the dentin. Theintegrated dip in the enamel curve yields a value of 714, while theintegrated dip in the dentin curve yields a value of 305. These valuesmay be used to construct standard calibration curves for the width ofdefects in enamel and dentin, assuming a sharp boundary between decayedand normal tooth structure. Revisiting the curves of FIGS. 21 and 24(extracted from an actual patient x-ray), measurable defect widths of1.4 mm in the enamel and 1.9 for the dentin are obtained, along withintegrated areas of 285 for the enamel and 299 for the dentin. Bycomparison with the composite calibration structure, defect widths of1.9 mm for the enamel and 2.3 mm for the dentin may be inferred orestimated. The integrated values correspond to a calibrated defectbetween about 1.5 and about 2.0 mm in width.

The calibration apparatus and methods described hereinabove may bemodified in a number of ways for improving diagnostic accuracy. Forexample, instead of void defects, the defects in the compositecalibration structure may be filled with a material simulating theradiodensity of partially decayed enamel or partially decayed dentin. Inanother example, the composite calibration structure may be made into amore realistic tooth shape, instead of a simple rectangle. Specificcomposite calibration structures may be made specific to each tooth, orspecific to the location of the decay on the tooth. The compositecalibration structure may be employed to optimize x-ray imageacquisition conditions (by analyzing images of the compositecalibration(s) structure(s) at varying exposure times, exposureintensities, and so on) to yield the best contrast between normal toothstructure and diseased or decayed tooth structure.

Optimized settings thus determined may be stored for repeated use, andmay be periodically re-determined and refreshed to compensate for agingof the x-ray source or x-ray imaging sensor.

Other dental pathologies may be simulated by suitably configuredcomposite calibration structures. Such other dental pathologies includebut are not limited to periodontal disease, endodontic disease, bonedensities around implants or implant failures, progression of diseasesby comparing prior images and data derived from those images, andpotentially the identification of tumors or lesions that might containcancer in the bone around teeth.

Software algorithms may also be employed for radiographic diagnosis orevaluation of periodontal disease. One example of such a softwarealgorithm may be designated for convenience as PerioScan CADD.

Periodontal disease (PD) is a tooth-born infection of a portion of thegums surrounding the teeth. Bacteria on the surface of teeth trigger aninflammatory response in the gum tissue around the teeth that mayeventually destroy the underlying crestal lamina dura bone around theteeth (FIGS. 75 and 76). Periodontal infections may contribute to otherserious diseases such as heart disease, implant infections, and strokes.However, early detection and treatment are effective means forpreventing these undesirable sequelae.

A main target market for treatment of periodontal disease is amongpeople age 40 and older. The potential market for treating periodontaldisease in the U.S. may range between $15 billion and $30 billionannually. A diagnostic system that encourages earlier and more accuratedetection will lead to higher levels of patient agreement to treatment,thus improving patient care as well as enhancing the dentist's revenuestream.

Currently, the most widely used assessment of periodontal disease ismanual probing of the gum tissue. The “probe” typically comprises ametal or plastic instrument between about 0.5 mm and about 1 mm indiameter that is manually inserted into the patient's gums around eachtooth. This is generally an uncomfortable or even painful procedure, andis also inherently inaccurate, since it is only an indirect assessmentof the underlying bone condition and is highly subjective (varying withboth clinician and patient). Subjective reading of dental x-ray orradiographs is often used to confirm periodontal disease, but typicallybone loss must be fairly far advanced (i.e. bone must be destroyed)before the damage can be readily seen upon visual inspection (FIGS.77-80). Unfortunately, bone destruction that has reached this stage istypically irreversible, again emphasizing the desirability of early,objective detection.

A software algorithm for analyzing digital dental radiographs mayprovide a more objective and more accurate means for diagnosing andevaluating periodontal disease. By providing objective numerical valuesfor characterizing periodontal disease, the software algorithm mayenable the clinician to make more appropriate treatment recommendations,and may elicit more ready acceptance of those treatment recommendationsby the patient.

In order to accurately diagnose and treat periodontal disease, aclinician must ascertain, inter alia: whether the disease is currentlyactive; if active, how aggressive is the infection; how much bone damagehas occurred; what is the prognosis if the disease is effectivelyeliminated. Further, the clinician must attempt to induce the patient tovisualize, comprehend, and concur with the findings and recommendedtreatment of the clinician. An objective two-number numerical scoringsystem provided by software analysis of digital radiographic images maybe employed to meet these requirements.

The first numerical value employed is the bone depth (BD). Patients arealready generally aware of “pocket depths” used for evaluatingperiodontal disease; these are the values obtained by manual probing ofgum tissue. Painless radiographic determination of bone depth is adesirable replacement for often painful manual probing, especially sincemanual probing to the full pocket depth in an area of disease can onlybe accurately determined when the patient is anesthetized in that area.The BD is typically expressed in mm from the cemento-enamel junction(CEJ), which may be readily identified and accurately located in anx-ray. A BD value of about 3 mm is desirable for an adult. Changes in BDcan be readily tracked over time to detect low-level chronic bone loss.A measured BD value over 4 mm is a direct indication that bone damagehas occurred, especially if the patient previously had a lower BD valuedetermined.

The second numerical value employed is Crestal Density (CD), which maybe used to detect and quantify the presence of active periodontaldisease. In the current example, CD is expressed on a 1 to 10+ scale (1indicating no periodontal disease with upper values ranging up to 15 oreven higher; any other desired scale range could be used). CD values aredetermined relative to healthy lamina dura around teeth and relative tonormal intramedullary bone density. Changes in CD may be readily trackedover time to detect periodontal disease in it earliest stages. On thescale used in this example, CD values of 1 to 3 are normal for healthyadults, CD values of 4 to 7 indicate thinning of crestal bone that maystill be halted with proper treatment, and CD values of 8 or moreindicate aggressive bone loss resulting in increased bone depth (BD)measurements.

Use of the software algorithm for measuring bone depth and crestaldensity from an x-ray is illustrated in FIGS. 81-89. First, the usermarks the image at the lamina dura on the facing surfaces of adjacentteeth (#30 and #31 in this example; FIGS. 81 and 82). Next, the usermarks opposing cemento-enamel junctions (CEJs) on the same teeth (FIGS.83 and 84). The line along which the software analyzes the crestal bonedensity runs between the midpoints of the segment connecting the laminadura of the adjacent teeth and the segment connecting the CEJs of theadjacent teeth (FIGS. 85-87). FIGS. 88 and 89 show a plot of bonedensity (i.e. radiographic density) along this analysis line, with themaximum density normalized to 100.

The bone depth (BD) may be extracted from the plot of FIG. 89 asfollows. The midpoint of the CEJ height line is the starting point foranalysis. The intramedullary bone density at the other end of theanalysis line is used as a reference density. Intramedullary bonedensity is averaged over a small area (several mm square, for example)to average out variation on small length scales. The bone depth isdefined as the distance along the analysis line from CEJ mid-point to apoint where the bone density has reached ½ of the intramedullary bonedensity (FIG. 90). In the example illustrated in FIGS. 81-89, a BD valueof about 2.5 mm is obtained, which indicates no present or pastperiodontal disease at this location.

The crestal density (CD) may be extracted from the plot of FIG. 89 asfollows. The bone depth point (the point where the plot reaches ½ of theintramedullary bone density) from the BD measurement serves as thestarting point for the analysis (FIG. 91). Peak bone density within thenext 1.5 mm along the analysis line starting at the ½ heightintramedullary density location is measured (FIG. 92). Peak lamina duradensity from the first two clicks (FIGS. 81 and 82) is measured from theimage and arbitrarily assigned a value of 1. The intramedullary bonedensity previously calculated (FIGS. 90 and 91) is arbitrarily assigneda value of 10. The peak density measured in the first 1.5 mm of crestalbone (FIG. 92) is scaled by comparison to the maximum density of thelamina dura (e.g., “1”) and the intramedullary bone density (e.g., “10”)to determine a relative CD value. Where no periodontal disease has beenpresent, the CD value obtained is 1 (FIG. 93). Both the BD and CD valuesare displayed for each location analyzed. The entire radiograph may bequickly analyzed as the operator clicks on the desired analysislocations, and the software performs the calculations described above inthe background (FIG. 94).

A site is indicated in FIG. 95 where there has been bone loss due toperiodontal disease. The procedure described above is followed forobtaining BD and CD values. The lamina dura locations and CEJ locationsare marked (FIGS. 96-99) and used to define the analysis line, alongwhich the bone density is plotted (FIG. 100). The bone depth (BD;measured from the CEJ segment midpoint to the ½ intramedullary densitypoint; FIG. 101) is about 5 mm, indicating significant bone loss haslikely already occurred. The peak bone depth within 1.5 mm of the BDposition is not as large as the intramedullary bone density (FIG. 102),yielding a CD value of about 12. This is indicative of active disease atthis location. Both BD and CD values may be displayed togethersuperimposed on the image, if desired (FIG. 103). Audible alarms orcolor-coded text or indicators may be employed in any desired manner toindicate the severity of disease. FIGS. 104-108 illustrate analysis ofanother site having active periodontal disease.

Reliability of the software algorithm for assessing periodontal diseaseis enhanced by use of reference points within the image. The density ofthe lamina dura is used as a high-density reference point, while theintramedullary bone is used as a low-density reference point. Thesedensities should generally be relatively unaffected by periodontaldisease. Since they are acquired in the same image as the diseaselocation, these densities provide a degree of normalization againstvariations of x-ray source, imaging x-ray sensor, exposure time orintensity, and so on.

While the values obtained for bone depth (BD) and crestal density (CD)provide accurate diagnosis and evaluation of periodontal disease, propertreatment of the disease also depends on the overall clinical setting,including the age of the patient. It may be desirable to factor thepatient's age directly into the calculation of the CD value. It also (orin the alternative) may be desirable for the clinician to determinetreatment for the patient based on age-neutral CD values whileindependently considering the patent's age.

For example, a 75-year-old patient presenting with the analyzedradiograph of FIG. 109 would typically require only routine prophylactictreatment with some extra cleaning between #14 & #15 and #20 & #21. FIG.110 shows the same radiograph analyzed as if obtained from a 50-year-oldpatient, with the CD values adjusted upward to reflect the patient'sage. The 50-year-old patient would benefit from full mouth scaling androot planing followed by a check at the next routine exam to verify thatCD had at least begun to return to normal values. If left untreated,bone loss will occur and BD values will increase for this patient. FIG.111 shows the same radiograph analyzed as if obtained from a 25-year-oldpatient, with the CD values adjusted upward accordingly. This patientrequires immediate interventional therapy and very close monitoring forthe next 12 to 18 months to determine if the infection has beeneliminated. Laser therapy or scaling, root planing, and antibiotics areindicated in this situation. Failure to treat this patient is likely toresult in early tooth loss. The adjustment of CD value upwards ordownward with age may be implemented in any suitable way that provides arational correlation between the CD value and the treatment indicatedfor a particular clinical presentation. By having such an adjustment forrisk factors (including but not limited to age), objective measurementof disease and more uniform treatment recommendations by doctors may bemade to the patient based upon treatment modalities that may optimallybenefit the patient.

The described procedure may be modified or adapted in a variety of ways.For example, image analysis, edge detection, or pattern recognition maybe used to locate the lamina dura locations or the CEJ locations. Asimplified “two-click” approach might be employed to create the analysisline: the CEJ height (click #1) and the intramedullary bone location(click #2). Rather than using the root lamina dura as a reference pointin the “4-click approach,” the rate of density change along the analysisline in combination with the average density of intramedullary bone maybe employed instead for calculating a CD value.

The present invention is also directed to a dental digital x-ray imagingcalibration method for at least partly correcting for variations of theoptical densities of images acquired from the dental digital x-rayimaging system. A simplified flow chart of the invention is shown inFIG. 112.

The calibration method of the present invention may include fiveexemplary basic steps.

As shown in block 200, the first step is providing at least onecalibration block or standard that simulates dental tissues. Preferablythe calibration block or standard has at least one simulated defecthaving a known numerical decay value pre-calculated from measuredoptical densities that correlate with the extent of the at least onesimulated defect. The numerical decay value can be pre-calculated by thesupplier (a provided known numerical decay value) or it can be obtainedupon initial acquisition of the calibration block or standard when it isin pristine condition. The calibration block or standard may be acomposite calibration block or standard. The calibration block orstandard may be real teeth with known levels of a particular defect. Thecalibration block or standard preferably simulates the true compositestructure of teeth including enamel, dentin, and pulp. The calibrationblock or standard preferably has a simulated defect that simulates toothdecay or caries. The calibration block or standard preferably has atleast one simulated defect that simulates dental pathology in both sizeand location. The calibration block or standard preferably has at leastone simulated defect that is filled with a material simulating theradiodensity of partially decayed enamel or partially decayed dentin. Inone preferred embodiment a plurality of calibration blocks or standardsare provided, each calibration block or standard having a differentsimulated defect.

As shown in block 202, the second step is acquiring an image of thecalibration block or standard from the dental digital x-ray imagingsystem.

As shown in block 204, the third step is calculating a calculatednumerical decay value from measured optical densities that correlatewith the extent of the simulated defect of the calibration block orstandard from which the image is acquired.

In one preferred embodiment of the present invention, the step ofcalculating a calculated numerical decay value is performed using asoftware algorithm.

As shown in block 206, the fourth step is comparing the known numericaldecay value and the calculated numerical decay value. In one preferredembodiment of the present invention, the step of comparing the knownnumerical decay value and the calculated numerical decay value isperformed using a software algorithm.

As shown in block 208, the fifth step is calibrating the dental digitalx-ray imaging system by adjusting the dental digital x-ray imagingsystem so that the calculated numerical decay value approaches the knownnumerical decay value. It should be noted that the calibration may bemade using any known correction technique including, but not limited tomechanical adjustments (e.g. focusing), software adjustments (e.g. usingsoftware algorithms to virtually make corrections), electricaladjustments (e.g. providing more or less power).

The calibration method of the present invention may be performed tooptimize x-ray image acquisition conditions including, but not limitedto exposure times, exposure intensities, protocols of image acquisition,and image processing algorithms.

The calibration method of the present invention may be performedwhenever there is a possible change in x-ray image acquisitionconditions. These changes include, but are not limited to: (a) aging,degradation, or change of the x-ray source; (b) aging, degradation, orchange of the x-ray imaging sensor; (c) aging, degradation, or change ofthe display monitor; (d) change in the protocol of image acquisition;(e) change in the image processing algorithm; and (d) at periodicintervals (e.g. every week, every year).

For the various procedures and algorithms described herein, the digitalimages analyzed are described as being acquired using a direct digitalimaging x-ray sensor. However, traditional film x-rays may be analyzedas well, by first scanning the film x-rays into a digital form.Additional variations may arise due to variability in the film, the filmdevelopment procedures, and the scanning process. Calibration proceduresdescribed herein may be employed to correct for these variations.

The various analysis procedures, calibrations procedures, or softwarealgorithms disclosed herein for dental or periodontal diagnosis mayprovide multiple benefits. Early diagnosis and accurate assessment ofdisease enable the clinician to recommend appropriate treatment in atimely fashion. Patients benefit from uniform, objective diagnosticstandards, thereby protecting them from under- or over-diagnosis.

The presentation of simple, numeric diagnostic values enables patientsto constructively participate in their diagnosis and treatment planning.Insurance companies benefit from uniform, objective diagnostic standardsto assure appropriate treatment and for screening for fraud by careproviders.

For purposes of the present disclosure and appended claims, theconjunction “or” is to be construed inclusively (e.g., “a dog or a cat”would be interpreted as “a dog, or a cat, or both”; e.g., “a dog, a cat,or a mouse” would be interpreted as “a dog, or a cat, or a mouse, or anytwo, or all three”), unless: i) it is explicitly stated otherwise, e.g.,by use of “either . . . or,” “only one of . . . ,” or similar language;or ii) two or more of the listed alternatives are mutually exclusivewithin the particular context, in which case “or” would encompass onlythose combinations involving non-mutually-exclusive alternatives. It isintended that equivalents of the disclosed exemplary embodiments andmethods shall fall within the scope of the present disclosure and/orappended claims. It is intended that the disclosed exemplary embodimentsand methods, and equivalents thereof, may be modified while remainingwithin the scope of the present disclosure or appended claims.

The terms and expressions that have been employed in the foregoingspecification are used as terms of description and not of limitation,and are not intended to exclude equivalents of the features shown anddescribed or portions of them. The scope of the invention is defined andlimited only by the claims that follow.

What is claimed is:
 1. A method for diagnosis and evaluation of toothdecay, said method comprising the steps of: (a) locating in an x-rayimage the contour of a dento-enamel junction (DEJ); (b) measuring atleast one optical density along contours substantially parallel to andon either side of the DEJ contour; and (c) calculating at least onenumerical decay value from the measured at least one optical density. 2.The method of claim 1, further comprising the step of calibrating thenumerical decay value, the bone depth, or the numerical crestal densityusing a radiograph of at least one composite calibration block.
 3. Themethod of claim 1, wherein said at least one numerical decay value issuitable for the diagnosis and evaluation of periodontal disease.
 4. Themethod of claim 1, further comprising the step of displaying said atleast one numerical decay value.
 5. The method of claim 4, furthercomprising the step of dynamically displaying said at least onenumerical decay value.
 6. The method of claim 5, further comprising thestep of dynamically displaying said at least one numerical decay valuein response to the position of a user-movable cursor.
 7. A method fordiagnosis and evaluation of tooth decay, said method comprising thesteps of: (a) locating in an x-ray image the contour of a dento-enameljunction (DEJ); (b) measuring at least one optical density alongcontours substantially parallel to and on either side of the DEJcontour; and (c) calculating at least one numerical decay value from themeasured at least one optical density; (d) wherein said at least onenumerical decay value is suitable for the diagnosis and evaluation oftooth decay.
 8. The method of claim 7, further comprising the step ofcalibrating the numerical decay value, bone depth, or numerical crestaldensity using a radiograph of at least one composite calibration block.